CN114474449A - Lignin/PBAT composite film material and preparation method and application thereof - Google Patents
Lignin/PBAT composite film material and preparation method and application thereof Download PDFInfo
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- CN114474449A CN114474449A CN202210327877.6A CN202210327877A CN114474449A CN 114474449 A CN114474449 A CN 114474449A CN 202210327877 A CN202210327877 A CN 202210327877A CN 114474449 A CN114474449 A CN 114474449A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B7/00—Mixing; Kneading
- B29B7/002—Methods
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
- C08H6/00—Macromolecular compounds derived from lignin, e.g. tannins, humic acids
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2497/00—Characterised by the use of lignin-containing materials
Abstract
The invention relates to a lignin/PBAT composite film material and a preparation method and application thereof. The preparation method comprises the steps of mixing specific lignin and PBAT together and hot-press molding; the weight average molecular weight of the specific lignin is 900-1700 g/mol, the dispersity coefficient is 1.2-1.4, and the content of phenolic hydroxyl groups is 3.5-5.5 mmol/g; the lignin/PBAT composite film material comprises 50-70% of PBAT and 30-50% of specific lignin in percentage by mass. The technical problem to be solved is how to add high-content (up to 50%) lignin into PBAT, so that the material cost of PBAT can be reduced, and the PBAT can also keep high tensile property (the tensile strength is more than or equal to 20MPa, and the elongation at break is more than or equal to 490%), thereby being more practical.
Description
Technical Field
The invention belongs to the technical field of biodegradable materials, and particularly relates to a lignin/PBAT composite film material as well as a preparation method and application thereof.
Background
In the production and life of modern society, the use ratio of plastic products is increasing. However, most of the plastic products used at present are made of non-degradable plastics, and the plastic products cannot be naturally degraded after being discarded, so that the long-term accumulation causes serious plastic pollution problems. Therefore, the use of the non-degradable plastics is reduced, and the development of green, environment-friendly and biodegradable plastics to replace the non-degradable plastics is of great significance to the environmental protection and the sustainable development of human beings.
Poly (butylene adipate terephthalate) (PBAT), a petroleum-based polyester plastic, has excellent biodegradability, flexibility and thermal stability, and is decomposed by enzymatic or chemical degradation of microorganisms (e.g., fungi, bacteria and algae) after being disposed in the natural environment, and further converted into carbon dioxide, methane, humus and other natural substances. Are currently used to produce bags for shopping, trash bags, agricultural mulching films, and the like. However, the high production cost of PBAT limits its further spread and application, and the addition of cheap, biodegradable fillers to reduce the production cost is an effective way.
Industrial lignin, a by-product of the pulp and paper industry and biorefinery industry, is produced in large quantities but has a low proportion of efficient utilization. If lignin can be used as a green filler of PBAT, the cost of PBAT products can be reduced, and high-value utilization of the lignin can be realized. However, in the prior art, when lignin is added to PBAT, the addition amount of lignin is low; if the addition amount of lignin is increased, the tensile property of PBAT is greatly reduced; and the addition of lignin with lower content has a very limited cost reduction for PBAT, and the lignin/PBAT composite material with high lignin addition amount and high tensile property is difficult to obtain.
Disclosure of Invention
The invention mainly aims to provide a lignin/PBAT composite film material and a preparation method and application thereof, and aims to solve the technical problem of adding higher content (up to 50%) of lignin into PBAT, so that the material cost of the PBAT can be reduced, and the PBAT can keep higher tensile property (the tensile strength is more than or equal to 20MPa, and the elongation at break is more than or equal to 490%), thereby being more practical.
The purpose of the invention and the technical problem to be solved are realized by adopting the following technical scheme. The preparation method of the lignin/PBAT composite film material provided by the invention comprises the steps of mixing specific lignin and PBAT together and hot-press molding; wherein the weight average molecular weight of the specific lignin is 900-1700 g/mol, the dispersity coefficient is 1.2-1.4, and the content of phenolic hydroxyl groups is 3.5-5.5 mmol/g.
The object of the present invention and the technical problems solved thereby can be further achieved by the following technical measures.
Preferably, in the preparation method, the specific lignin is separated from the industrial lignin raw material by a solvent extraction method, and the specific steps are as follows:
2-1) dissolving an industrial lignin raw material in an ethyl acetate solvent, and stirring for 4-8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the industrial lignin raw material to the ethyl acetate solvent is 1 g: 5-10 ml;
2-2) carrying out suction filtration on the solution, and concentrating and drying the filtrate to obtain the specific lignin.
Preferably, in the preparation method, the specific lignin is separated from the industrial lignin raw material by a solvent precipitation method, and the specific steps are as follows:
3-1) dissolving an industrial lignin raw material in an absolute ethyl alcohol solvent, and stirring for 4-8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the industrial lignin raw material to the absolute ethyl alcohol solvent is 1 g: 5-10 ml;
3-2) adding distilled water into the solution to adjust the volume concentration of ethanol to 50%, and performing centrifugal separation to obtain a supernatant;
3-3) adding distilled water into the supernatant to adjust the volume concentration of ethanol to 35-45%, performing centrifugal separation, taking the precipitate, grinding and drying to obtain the specific lignin.
Preferably, in the above method, the industrial lignin raw material is at least one selected from the group consisting of kraft lignin, alkali lignin and prehydrolysis liquid lignin.
Preferably, in the preparation method, in the mixing of the specific lignin and the PBAT, the mass percentage ratio of the specific lignin to the PBAT is 30-50%: 50% -70%; the total amount of the specific lignin and the PBAT is 100%.
Preferably, in the preparation method, the mixing is performed by using at least one of an extruder, an open mill and an internal mixer; the mixing temperature is 130-150 ℃, and the mixing time is 30-60 min.
The object of the present invention and the technical problem to be solved are also achieved by the following technical means. According to the lignin/PBAT composite film material provided by the invention, the lignin/PBAT composite film material consists of 50-70% of PBAT and 30-50% of specific lignin in percentage by mass; wherein the weight average molecular weight of the specific lignin is 900-1700 g/mol, the molecular weight dispersity coefficient is 1.2-1.4, and the content of phenolic hydroxyl is 3.5-5.5 mmol/g.
The object of the present invention and the technical problems solved thereby can be further achieved by the following technical measures.
Preferably, the tensile strength of the lignin/PBAT composite film material is more than or equal to 20MPa, and the breaking elongation of the lignin/PBAT composite film material is more than or equal to 490 percent.
Preferably, the lignin/PBAT composite film material is prepared according to the preparation method.
The object of the present invention and the technical problem to be solved are also achieved by the following technical means. According to the application of the lignin/PBAT composite film material in the fields of agricultural mulching films, garbage covering films and packaging materials, the invention provides a method for preparing a lignin/PBAT composite film material.
By means of the technical scheme, the lignin/PBAT composite film material and the preparation method and application thereof provided by the invention have the following advantages:
the invention provides a lignin/PBAT composite film material and a preparation method and application thereof, the method separates specific lignin regulated by structure from industrial lignin raw materials, wherein the weight average molecular weight of the specific lignin is between 900 and 1700 g/mol, the molecular weight dispersity coefficient is 1.2-1.4, the phenolic hydroxyl group content is 3.5-5.5 mmol/g, the specific lignin regulated by the structure has lower glass transition temperature (the glass transition temperature is less than 95 ℃) which is far lower than the glass transition temperature of the industrial lignin raw material, and the processing temperature is much lower than the general processing temperature of the lignin/PBAT composite film material, so the specific lignin and the PBAT which are regulated and controlled by the structure are used for blending, the lignin/PBAT composite film material has better melt mixing property at the processing temperature, thereby being beneficial to improving the tensile property of the lignin/PBAT composite material; the lignin with the weight-average molecular weight of more than 1700 g/mol has higher glass transition temperature, is not easy to be well melted and mixed with PBAT, and can not keep better tensile property when being added with higher content; the lignin with the weight-average molecular weight less than 900 g/mol has low glass transition temperature, but because the molecular weight is too low, the condensation phenomenon among lignin molecules exists in the thermal processing process of preparing the lignin/PBAT composite material, so that the molecular weight of the lignin with the originally smaller molecular weight is increased after the thermal processing, the aggregation among the lignin molecules is promoted, and the tensile property of the prepared lignin/PBAT composite material is reduced; furthermore, the specific lignin has a small molecular weight dispersion coefficient (1.2-1.4), good structural uniformity and more consistent performance in the thermal processing process, so that the defect that one part of lignin is molten and the other part of lignin is not molten is avoided; furthermore, the content of phenolic hydroxyl groups of the specific lignin is moderate (3.5-5.5 mmol/g), on one hand, a certain amount of phenolic hydroxyl groups need to be kept in the specific lignin, and the phenolic hydroxyl groups can promote the formation of hydrogen bond between the lignin and PBAT, so that the tensile property of the composite material is improved, on the other hand, the content of the phenolic hydroxyl groups cannot be too high, because the content of the phenolic hydroxyl groups can influence the glass transition temperature of the lignin, when the content of the phenolic hydroxyl groups is too high, the interaction force inside the lignin is increased, mainly hydrogen bonds, so that the glass transition temperature of the lignin is improved, and the tensile property of the lignin/PBAT composite material is influenced; according to the invention, specific lignin which is regulated and controlled by a structure is separated from industrial lignin raw materials, and is mixed with PBAT and subjected to hot press molding, so that the lignin/PBAT composite material which is free of lignin chemical modification, free of any additive, and capable of simultaneously having high lignin addition amount (up to 50%) and high tensile property (tensile strength is greater than or equal to 20MPa and elongation at break is greater than or equal to 490%) is obtained by only utilizing the physical and chemical properties of the industrial lignin, the cost of the PBAT biodegradable material is greatly reduced, and the popularization and application of the PBAT biodegradable material and the high-value utilization of the lignin are facilitated.
The foregoing is a summary of the present invention, and in order to provide a clear understanding of the technical means of the present invention and to be implemented in accordance with the present specification, the following is a detailed description of the preferred embodiments of the present invention.
Drawings
Fig. 1 is a drawing for observing the morphology of quenched sections of the composite thin film materials in example 5 and comparative examples 1 to 3 by SEM;
FIG. 2 is a two-dimensional HSQC spectrum of the lignin obtained in comparative example 5 before and after thermal processing.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description will be made in conjunction with the preferred embodiments of a lignin/PBAT composite film material, a preparation method thereof, and specific embodiments, structures, characteristics and effects thereof according to the present invention.
The invention provides a specific lignin regulated and controlled by a structure, wherein the weight average molecular weight range of the specific lignin is 900-1700 g/mol, the molecular weight dispersity coefficient is 1.2-1.4, and the content of phenolic hydroxyl groups is 3.5-5.5 mmol/g.
The invention also provides a lignin/PBAT composite film material which comprises 50-70% of PBAT and 30-50% of specific lignin regulated and controlled by a structure in percentage by mass; wherein the weight average molecular weight range of the specific lignin subjected to structure regulation is 900-1700 g/mol, the molecular weight dispersity coefficient is 1.2-1.4, and the phenolic hydroxyl group content is 3.5-5.5 mmol/g.
The invention also provides a preparation method of the lignin/PBAT composite film material, which comprises the steps of mixing specific lignin with the weight-average molecular weight of 900-1700 g/mol, the molecular weight dispersity coefficient of 1.2-1.4 and the phenolic hydroxyl content of 3.5-5.5 mmol/g with PBAT, and carrying out hot press molding to obtain the lignin/PBAT composite film material.
According to the technical scheme, the specific lignin and the PBAT which are regulated and controlled by the structure are mixed and subjected to hot press molding, so that the lignin/PBAT composite material which is free of lignin chemical modification, free of any auxiliary agent addition, and capable of simultaneously having high lignin addition amount (up to 50%) and high tensile property (tensile strength is larger than or equal to 20Mpa and elongation at break is larger than or equal to 490%) is obtained by only utilizing the physicochemical properties of the industrial lignin, the cost of the PBAT biodegradable material is greatly reduced, and popularization and application of the PBAT biodegradable material and high-value utilization of the lignin are facilitated.
The weight average molecular weight of the specific lignin regulated by the structure is moderate, the glass transition temperature is lower than 95 ℃, the glass transition temperature is far lower than the glass transition temperature of an industrial lignin raw material, and the glass transition temperature is much lower than the common processing temperature (130-150 ℃) of a lignin/PBAT composite film material, so that when the specific lignin regulated by the structure is used for blending with the PBAT, the specific lignin has better melting mixing property at the processing temperature of the lignin/PBAT composite film material, and the tensile property of the lignin/PBAT composite material is improved; in addition, the lignin in the structural range can also avoid the adverse effect of the condensation phenomenon in the thermal processing process on the tensile property of the lignin/PBAT composite material; when the weight average molecular weight of the lignin is more than 1700 g/mol, the glass transition temperature of the lignin is higher, and the lignin is not easy to be well melted and mixed with PBAT, so that the technical effect of the invention is difficult to realize; when the weight average molecular weight of the lignin is less than 900 g/mol, although the glass transition temperature of the lignin is low, the molecular weight of the lignin is too low, and a condensation phenomenon among lignin molecules exists in the thermal processing process of preparing the lignin/PBAT composite material, so that the molecular weight of the lignin with the originally small molecular weight is increased after the thermal processing, the aggregation among the lignin molecules is promoted, and the tensile property of the prepared lignin/PBAT composite material is reduced.
The molecular weight dispersion coefficient of the specific lignin regulated and controlled by the structure is 1.2-1.4, the structure uniformity is good, and all points are basically synchronous in the hot processing process of blending and hot pressing of the composite material, so that the defect of poor local melting effect in the composite material is overcome.
The content of phenolic hydroxyl groups of the specific lignin regulated by the structure is 3.5-5.5 mmol/g, and the contained phenolic hydroxyl groups can promote the lignin and PBAT to form interaction force so as to improve the tensile property of the composite material; however, if the phenolic hydroxyl group content is too high, the interaction force such as hydrogen bonding formed inside the lignin increases, the glass transition temperature thereof increases, and the tensile properties of the lignin/PBAT composite material are affected.
The structurally-modified lignin can be isolated from industrial lignin feedstocks by a variety of methods, with preferred methods including solvent extraction and solvent precipitation.
The invention also provides a method for separating the specific lignin regulated by the structure from the industrial lignin raw material by a solvent extraction method. The solvent extraction method comprises the following specific steps: dissolving an industrial lignin raw material in an ethyl acetate solvent, and stirring for 4-8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the industrial lignin raw material to the ethyl acetate solvent is 1 g: 5-10 ml; after stirring, carrying out suction filtration on the mixed solution to obtain an ethyl acetate solution of lignin and lignin residues insoluble in ethyl acetate; and concentrating and drying the ethyl acetate solution of the lignin to obtain the specific lignin regulated and controlled by the structure. For comparison, the stirring time in the examples and comparative examples of the invention is 8h, and the solid-to-liquid ratio of the industrial lignin raw material to the ethyl acetate solvent is 1 g: 10 ml.
The invention also provides a method for separating the specific lignin regulated by the structure from the industrial lignin raw material by a solvent precipitation method. The solvent precipitation method comprises the following specific steps: dissolving an industrial lignin raw material in an absolute ethyl alcohol solvent, and stirring for 4-8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the industrial lignin raw material to the absolute ethyl alcohol solvent is 1 g: 5-10 ml; after stirring, carrying out suction filtration on the mixed solution to obtain an absolute ethyl alcohol solution of lignin and lignin residues insoluble in absolute ethyl alcohol; adding distilled water into the lignin absolute ethyl alcohol solution, and adjusting the ethyl alcohol in the lignin solution to a certain concentration so as to precipitate the lignin with high molecular weight dissolved in the lignin absolute ethyl alcohol solution; continuously adding distilled water into the lignin solution after the precipitate is removed, and adjusting the ethanol in the lignin solution to another concentration so as to precipitate the lignin with higher molecular weight dissolved in the lignin ethanol solution; and (4) continuing the steps for several times, so that the industrial lignin raw material can be separated into several lignin with different structures. According to the invention, distilled water is preferably added into the absolute ethyl alcohol solution of the lignin to adjust the volume concentration of the ethyl alcohol in the lignin solution to 50%, and the supernatant is obtained after centrifugal separation; and then adding distilled water into the supernatant to adjust the volume concentration of ethanol to 35-45%, performing centrifugal separation, taking the precipitate, grinding and drying to obtain the specific lignin. For comparison, the stirring time in the examples and comparative examples of the invention is 8h, and the solid-to-liquid ratio of the industrial lignin raw material to the absolute ethanol solvent is 1 g: 10 ml; when the solvent is precipitated, the volume concentration of the ethanol for the first time is 50 percent, and the volume concentration of the ethanol for the last time is 40 percent.
The industrial lignin raw material in the technical scheme of the invention is at least one selected from sulfate lignin, alkali lignin and prehydrolysis liquid lignin.
The mixing in the technical scheme of the invention is carried out by adopting at least one of an extruder, an open mill and an internal mixer; the mixing temperature is 130-150 ℃, and the mixing time is 30-60 min. For comparison, the mixing temperature in the examples and comparative examples of the present invention was 140 ℃ and the mixing time was 30 min.
The invention also provides application of the lignin/PBAT composite film material in the fields of agricultural mulching films, garbage covering films and packaging materials. Agricultural plastic film, rubbish cover film and wrapping bag all have better tensile properties.
The present invention will be further described with reference to the following specific examples, which should not be construed as limiting the scope of the invention, but rather as providing those skilled in the art with certain insubstantial modifications and adaptations of the invention based on the teachings of the invention set forth herein.
Unless otherwise specified, the following materials, reagents and the like are commercially available products well known to those skilled in the art; unless otherwise specified, all methods are well known in the art. Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.
Example 1
1) Extracting specific lignin with regulated structure by solvent extraction method
Dissolving alkali lignin in ethyl acetate solvent, and stirring in a constant-temperature water bath at 25 ℃ for 8 h; wherein the solid-to-liquid ratio of the alkali lignin to the ethyl acetate solvent is 1 g: 10 ml; after stirring, carrying out suction filtration on the mixed solution to obtain an ethyl acetate solution of lignin; concentrating and drying the ethyl acetate solution of the lignin to obtain the specific lignin regulated and controlled by the structure, wherein the structure characteristic is as follows: the weight average molecular weight is 1230 g/mol, the molecular weight dispersity coefficient is 1.25, and the phenolic hydroxyl group content is 3.61 mmol/g.
2) 30 parts by mass of specific lignin subjected to structural regulation and control and 70 parts by mass of poly (butylene adipate terephthalate) (PBAT) particles are mixed in an open mill to prepare the composite master batch. The open mill processing parameters were as follows: the heating temperature was set at 140 ℃, the roller speed was set at 30 Hz, and the open time was set at 30 min.
3) And (3) carrying out hot pressing on the composite master batch to form a film, thus obtaining the lignin/PBAT composite film material.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally controlled, of this example are shown in table 1.
Example 2
1) Extracting specific lignin with regulated structure by solvent precipitation method
Dissolving alkali lignin in an absolute ethyl alcohol solvent, and stirring in a constant-temperature water bath at 25 ℃ for 8 hours; wherein the solid-to-liquid ratio of the alkali lignin to the ethyl acetate solvent is 1 g: 10 ml; after stirring, carrying out suction filtration on the mixed solution to obtain an absolute ethyl alcohol solution of lignin; adding distilled water into the absolute ethyl alcohol solution of the lignin, adjusting the volume concentration of the ethyl alcohol in the lignin solution to 50%, performing centrifugal separation, and taking supernatant; then adding distilled water into the supernatant to adjust the volume concentration of ethanol to 40%, centrifugally separating, grinding and drying the precipitate component to obtain the specific lignin regulated and controlled by the structure, wherein the structure characteristic is as follows: the weight average molecular weight was 1420 g/mol, the molecular weight dispersibility coefficient was 1.29, and the phenolic hydroxyl group content was 3.89 mmol/g.
2) 30 parts by mass of specific lignin subjected to structural regulation and control and 70 parts by mass of poly (butylene adipate terephthalate) (PBAT) particles are mixed in an open mill to prepare the composite master batch. The open mill processing parameters were as follows: the heating temperature was set at 140 ℃, the roller speed was set at 30 Hz, and the open time was set at 30 min.
3) And (3) carrying out hot pressing on the composite master batch to form a film, thus obtaining the lignin/PBAT composite film material.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally controlled, of this example are shown in table 1.
Example 3
Step 1) the same as example 1, wherein the industrial lignin raw material selects prehydrolysis liquid lignin; the structural characteristics of the resulting structurally-modulated specific lignin are as follows: the weight average molecular weight is 970 g/mol, the molecular weight dispersity coefficient is 1.35, and the phenolic hydroxyl group content is 5.23 mmol/g.
Step 2) and step 3) are the same as in example 1.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally controlled, of this example are shown in table 1.
Example 4
Step 1) as in example 2, wherein the prehydrolysis liquid lignin is selected as the industrial lignin raw material, and the structural characteristics of the obtained specific lignin regulated and controlled by the structure are as follows: the weight average molecular weight was 1150 g/mol, the molecular weight dispersibility coefficient was 1.39, and the phenolic hydroxyl group content was 5.46 mmol/g.
Step 2) and step 3) are the same as in example 2.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally controlled, of this example are shown in table 1.
Example 5
Step 1) the same as example 1, wherein the industrial lignin raw material is kraft lignin; the structural characteristics of the resulting structurally-modulated specific lignin are as follows: the weight average molecular weight was 1530 g/mol, the molecular weight dispersibility coefficient was 1.30, and the phenolic hydroxyl group content was 4.12 mmol/g.
Step 2) and step 3) are the same as in example 1.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally controlled, of this example are shown in table 1. A Scanning Electron Microscope (SEM) of a quenched section of the lignin/PBAT composite film material prepared in this example is shown as a in fig. 1.
Example 6
Step 1) the same as example 2, wherein the industrial lignin raw material is kraft lignin, and the obtained specific lignin with a regulated structure has the following structural characteristics: the weight average molecular weight is 1690 g/mol, the molecular weight dispersity coefficient is 1.37, and the phenolic hydroxyl group content is 4.62 mmol/g.
Step 2) and step 3) are the same as in example 2.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally controlled, of this example are shown in table 1.
Example 7
Step 1) is the same as in example 1.
Step 2) as in example 1, wherein the mass ratio of the structurally-controlled specific lignin to the poly (butylene adipate terephthalate) (PBAT) particles was 40: 60.
Step 3) the same as in example 1.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally controlled, of this example are shown in table 1.
Example 8
Step 1) is the same as in example 4.
Step 2) as in example 4, wherein the mass ratio of the structurally-controlled specific lignin to the poly (butylene adipate terephthalate) (PBAT) particles was 50: 50.
Step 3) the same as in example 4.
The results of the glass transition temperature (Tg 1) of the specific lignin, the glass transition temperature (Tg 2) of the lignin/PBAT composite film material, and the tensile strength and elongation at break of the lignin/PBAT composite film material, which are structurally regulated in the present example, are shown in table 1.
Comparative example 1
30 parts by mass of dry kraft lignin and 70 parts by mass of poly (adipic acid)/butylene terephthalate (PBAT) particles are mixed and milled to prepare the composite master batch. The open mill processing parameters were as follows: the heating temperature was set at 140 ℃, the roller rotation speed was set at 30 Hz, and the open time was set at 30 min.
And (3) carrying out hot pressing on the composite master batch to form a film, thus obtaining the lignin/PBAT composite film material.
The results of the glass transition temperature of the lignin (Tg 1), the glass transition temperature of the lignin/PBAT composite film material (Tg 2), and the tensile strength and elongation at break of the lignin/PBAT composite film material of the present comparative example are shown in table 1. The Scanning Electron Microscopy (SEM) of the quenched section of the lignin/PBAT composite film material prepared by the comparative example is shown as b in figure 1.
Comparative example 2
In the same manner as in comparative example 1, 30 parts by mass of dried prehydrolysis liquid lignin was selected as the lignin.
The results of the glass transition temperature of lignin (Tg 1), the glass transition temperature of the lignin/PBAT composite film material (Tg 2), and the tensile strength and elongation at break of the lignin/PBAT composite film material of the present comparative example are shown in table 1. The Scanning Electron Microscopy (SEM) of the quenched section of the lignin/PBAT composite film material prepared by the comparative example is shown as c in FIG. 1.
Comparative example 3
In the same manner as in comparative example 1, 30 parts by mass of dried alkali lignin was used as the lignin.
The results of the glass transition temperature of the lignin (Tg 1), the glass transition temperature of the lignin/PBAT composite film material (Tg 2), and the tensile strength and elongation at break of the lignin/PBAT composite film material of the present comparative example are shown in table 1. The Scanning Electron Microscopy (SEM) of the quenched section of the lignin/PBAT composite film material prepared by the comparative example is shown as d in figure 1.
Comparative example 4
In the same manner as in example 6, the step of extracting the specific lignin with a structure-controlled by a solvent precipitation method was as follows: dissolving the kraft lignin in an absolute ethyl alcohol solvent, and stirring for 8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the alkali lignin to the ethyl acetate solvent is 1 g: 10 ml; after stirring, carrying out suction filtration on the mixed solution to obtain an absolute ethyl alcohol solution of lignin; adding distilled water into the absolute ethyl alcohol solution of the lignin, adjusting the volume concentration of the ethyl alcohol in the lignin solution to 35%, performing centrifugal separation, and taking supernatant; then adding distilled water into the supernatant to adjust the volume concentration of ethanol to 30%, centrifugally separating, grinding and drying the precipitate component to obtain the specific lignin regulated and controlled by the structure, wherein the structure characteristic is as follows: the weight average molecular weight is 835 g/mol, the molecular weight dispersity coefficient is 1.25, and the phenolic hydroxyl group content is 3.06 mmol/g.
The results of the glass transition temperature of the lignin (Tg 1), the glass transition temperature of the lignin/PBAT composite film material (Tg 2), and the tensile strength and elongation at break of the lignin/PBAT composite film material of the present comparative example are shown in table 1.
Comparative example 5
In the same manner as in example 6, the step of extracting the specific lignin with a structure-controlled by a solvent precipitation method was as follows: dissolving the kraft lignin in an absolute ethyl alcohol solvent, and stirring for 8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the alkali lignin to the ethyl acetate solvent is 1 g: 10 ml; after stirring, carrying out suction filtration on the mixed solution to obtain an absolute ethyl alcohol solution of lignin; adding distilled water into the absolute ethyl alcohol solution of the lignin, adjusting the volume concentration of the ethyl alcohol in the lignin solution to 30%, performing centrifugal separation, and taking supernatant; then adding distilled water into the supernatant to adjust the volume concentration of the ethanol to 20%, centrifugally separating, grinding and drying the precipitate component to obtain the specific lignin with the structure regulated and controlled, wherein the specific lignin has the following structural characteristics: the weight average molecular weight was 753 g/mol, the molecular weight dispersity coefficient was 1.28, and the phenolic hydroxyl group content was 2.89 mmol/g.
The results of the glass transition temperature of the lignin (Tg 1), the glass transition temperature of the lignin/PBAT composite film material (Tg 2), and the tensile strength and elongation at break of the lignin/PBAT composite film material of the present comparative example are shown in table 1. FIG. 2 is a two-dimensional HSQC spectrum of the lignin obtained in comparative example 5 before and after thermal processing, wherein a) is the lignin before thermal processing, B) is the lignin after thermal processing, the structural formula A is a beta-O-4 bond structure, and the structural formula B is a condensed beta-beta bond structure.
Comparative example 6
The same as example 5, wherein methanol was used as the solvent. The structural characteristics of the resulting structurally-modulated specific lignin are as follows: the weight average molecular weight is 2810 g/mol, the molecular weight dispersity coefficient is 1.54, and the phenolic hydroxyl group content is 3.43 mmol/g.
The results of the glass transition temperature of the lignin (Tg 1), the glass transition temperature of the lignin/PBAT composite film material (Tg 2), and the tensile strength and elongation at break of the lignin/PBAT composite film material of the present comparative example are shown in table 1.
Performance test method
And (3) detecting the tensile property: determination of tensile Properties of plastics according to the national Standard GB/T1040.2-2006 part 2: test conditions for molded and extruded plastics the tensile properties of all the above composite film materials were measured, and at least 5 measurements were taken per sample, and the average was taken.
The weight average molecular weight and the molecular weight dispersion coefficient of the lignin are detected by adopting high pressure liquid chromatography, and the method comprises the following specific operations: weighing 4 mg lignin sample, dissolving in 2 mL tetrahydrofuran, filtering the solution with 0.22 μ L polyethylene filter head, and analyzing with chromatographic column. Molecular weight size of lignin samples was calculated based on the standard curve of the standards, with molecular weights of 435500, 66000, 9200, and 1320 g/mol for the 4 polystyrene standards.
The method for detecting the content of the phenolic hydroxyl groups of the lignin adopts quantitative phosphorus spectrum measurement and specifically comprises the following operations: weighing 20 mg of lignin sample, dissolving in 500. mu.L of anhydrous pyridine/CDCl 3 mixed solvent (v/v 1.6: 1), after completely dissolving the lignin, sequentially adding 100. mu.L of chromium (III) acetylacetonate solution and 100. mu.L of cyclohexanol solution, respectively serving as relaxation agent and internal standard, and finally adding 100. mu.L of 2-chloro-4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaphosphonic acid (TMDP) serving as phosphating agent to carry out phosphating treatment on the lignin sample.
The detection of the glass transition temperature adopts a Differential Scanning Calorimeter (DSC) for testing, and the specific operation is as follows: raising the temperature from room temperature to 180 ℃ at a heating rate of 10 ℃/min, and keeping the temperature for 5 min to eliminate the thermal history; then the temperature is decreased to 80 ℃ at the rate of 10 ℃/min and is kept constant for 2min, and then the temperature is increased to 220 ℃ at the rate of 10 ℃/min. The gas flow rate is 50 mL/min, 5.0 mg of the sample is weighed, and the instrument adopts liquid nitrogen for refrigeration.
TABLE 1
| Tensile Strength (MPa) | Elongation at Break (%) | Tg1（℃） | Tg2（℃） | |
| Pure PBAT | 31.16 | 801.23 | -- | -33.1 |
| Example 1 | 26.09 | 696.92 | 86.3 | -8.4 |
| Example 2 | 24.52 | 635.76 | 87.2 | -12.7 |
| Example 3 | 26.26 | 654.17 | 78.7 | -8.5 |
| Example 4 | 23.75 | 605.82 | 83.6 | -14.6 |
| Example 5 | 26.68 | 697.53 | 90.6 | -9.6 |
| Example 6 | 23.61 | 591.93 | 94.2 | -15.1 |
| Example 7 | 22.51 | 546.38 | 86.3 | -2.0 |
| Example 8 | 20.21 | 494.73 | 83.6 | -4.2 |
| Comparative example 1 | 10.86 | 62.03 | 193.5 | -25.4 |
| Comparative example 2 | 13.41 | 179.64 | 142.5 | -24.2 |
| Comparative example 3 | 11.74 | 124.36 | 165.2 | -26.2 |
| Comparative example 4 | 15.42 | 287.56 | 76.1 | -17.1 |
| Comparative example 5 | 14.63 | 246.15 | 68.3 | -19.2 |
| Comparative example 6 | 11.27 | 62.49 | 177.2 | -27.2 |
From the test data in table 1, it can be seen that, under the same amount of added lignin, the specific lignin with a controlled structure obtained by the solvent extraction method and the solvent precipitation method of the present invention, and the lignin/PBAT composite film material prepared by mixing with PBAT and hot press forming have better tensile properties than the industrial lignin raw material directly and the composite film material prepared by mixing with PBAT and hot press forming, as shown in example 5, example 6 and comparative example 1. The result shows that the specific lignin regulated and controlled by the structure can effectively improve the tensile property of the lignin/PBAT composite film material and can still maintain higher tensile property under the condition of higher addition amount. Furthermore, the specific lignin which is obtained by the solvent extraction method and the solvent precipitation method and is subjected to structure regulation has better effects on sulfate lignin, prehydrolysis liquid lignin and alkali lignin. Furthermore, when the specific lignin which is obtained by the solvent extraction method and the solvent precipitation method and is subjected to structure regulation and control is used for mixing with PBAT and hot-press molding to prepare a composite film material, the tensile property of the specific lignin can still keep a good level even under the condition that the addition amount of the specific lignin is up to 50 percent, and the tensile strength is more than 20MPa and the elongation at break is more than 490 percent. Further, as can be seen from the Tg2 values in table 1, the addition of lignin results in an increase in the glass transition temperature of the composite. Indicating that certain hydrogen bonding is formed between the added lignin molecules and PBAT molecules. From the Tg2 of examples 1-6 and comparative examples 1-6, the composite materials made with lignin within the structural feature range had a Tg2 higher than the Tg2 of the composite materials made with lignin outside the structural feature. This suggests that lignin within the structural features is able to form stronger hydrogen bonding with PBAT. Therefore, the composite material prepared by the lignin in the structural characteristic range has better stress transmission in the stretching process, and is beneficial to improving the stretching performance of the composite material.
As can be seen from the SEM images of the quenched section morphology of the composite thin film materials in example 5 and comparative examples 1 to 3 shown in fig. 1, a in fig. 1 has a more compact and flat section compared to b, c and d in fig. 1, and at the same time, the existence of the lignin particle aggregation region is not seen in the section of a, which indicates that the specific lignin within the characteristic structure range proposed by the present invention has better miscibility with PBAT, so that the specific lignin regulated by the structure can obtain better tensile property when blended with PBAT.
As shown in the attached figure 2, the two-dimensional HSQC spectrum of the small-molecular lignin (weight average molecular weight < 900) in the comparative example 5 is shown as a) in the attached figure 2, and the structural units of the small-molecular lignin mainly comprise beta-O-4 connecting bonds, and have a structure shown as A in the figure; during the high-temperature blending and hot-pressing film making process, due to the action of heat treatment, the small-molecule lignin is condensed to form a condensed beta-beta connecting bond (such as a structure shown as B in figure 2), and a corresponding two-dimensional HSQC spectrogram is shown as B in figure 2. The condensation phenomenon of the small-molecular lignin in thermal processing can cause the aggregation of the lignin, thereby reducing the tensile property of the prepared lignin/PBAT composite material.
The features of the invention claimed and/or described in the specification may be combined, and are not limited to the combinations set forth in the claims by the recitations therein. The technical solutions obtained by combining the technical features in the claims and/or the specification also belong to the scope of the present invention.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are still within the scope of the technical solution of the present invention.
Claims (10)
1. A preparation method of a lignin/PBAT composite film material is characterized by comprising the steps of mixing specific lignin and PBAT together and carrying out hot press molding; wherein the weight average molecular weight of the specific lignin is 900-1700 g/mol, the dispersity coefficient is 1.2-1.4, and the phenolic hydroxyl group content is 3.5-5.5 mmol/g.
2. The method for preparing lignin according to claim 1, wherein the specific lignin is separated from industrial lignin raw material by solvent extraction method, comprising the following steps:
2-1) dissolving an industrial lignin raw material in an ethyl acetate solvent, and stirring for 4-8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the industrial lignin raw material to the ethyl acetate solvent is 1 g: 5-10 ml;
2-2) carrying out suction filtration on the solution, and concentrating and drying the filtrate to obtain the specific lignin.
3. The preparation method according to claim 1, wherein the specific lignin is separated from the industrial lignin raw material by a solvent precipitation method, and the specific steps are as follows:
3-1) dissolving an industrial lignin raw material in an absolute ethyl alcohol solvent, and stirring for 4-8 hours in a constant-temperature water bath at 25 ℃; wherein the solid-to-liquid ratio of the industrial lignin raw material to the absolute ethyl alcohol solvent is 1 g: 5-10 ml;
3-2) adding distilled water into the solution to adjust the volume concentration of ethanol to 50%, and performing centrifugal separation to obtain a supernatant;
3-3) adding distilled water into the supernatant to adjust the volume concentration of ethanol to 35-45%, performing centrifugal separation, taking the precipitate, grinding and drying to obtain the specific lignin.
4. The method according to claim 2 or 3, wherein the industrial lignin raw material is at least one selected from kraft lignin, alkali lignin and prehydrolysis liquid lignin.
5. The preparation method according to claim 1, wherein in the mixing of the specific lignin and the PBAT, the mass percentage ratio of the specific lignin to the PBAT is 30-50% in terms of mass percentage: 50% -70%; the total amount of the specific lignin and the PBAT is 100%.
6. The method of claim 1, wherein the mixing is performed using at least one of an extruder, an open mill, and an internal mixer; the mixing temperature is 130-150 ℃, and the mixing time is 30-60 min.
7. The lignin/PBAT composite film material is characterized by comprising 50-70% of PBAT and 30-50% of specific lignin in percentage by mass; wherein the weight average molecular weight of the specific lignin is 900-1700 g/mol, the molecular weight dispersity coefficient is 1.2-1.4, and the content of phenolic hydroxyl is 3.5-5.5 mmol/g.
8. The lignin/PBAT composite film material according to claim 7, wherein the tensile strength is not less than 20MPa, and the elongation at break is not less than 490%.
9. The lignin/PBAT composite film material according to claim 7 or 8, which is prepared by the preparation method according to any one of claims 1 to 6.
10. Use of the lignin/PBAT composite film material according to any one of claims 7 to 9 in the field of agricultural mulching films, garbage covering films and packaging materials.
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